Tumor development and progression has long been known to involve both genetic and epigenetic alterations in the gene expression profile of tumor cells. Of particular importance is the silencing of tumor suppressor genes. Epigenetic mechanisms of gene silencing include histone deacetylation, DMA methylation, and histone methylation. Each of these mechanisms are interrelated and influence each other. Inhibitors of both histone deacetylation and DMA methylation are available and are in use as promising anti-cancer agents. However, only recently has the role of histone methylation become apparent. H3-K9 methyltransferases have been linked to the function of tumor suppressor genes, cellular senescence and regulating telomere length. In both breast and prostate cancer the H3-K27 methyltransferase EZH2 is over-expressed and is a strong prognostic factor for aggressive or metastatic tumors. In addition specific transcription factors recruit individual histone methyltransferases necessary for their gene silencing function. These rapidly developing links between histone methylation and tumors and cell growth control suggest an exciting new therapeutic target. However, existing technologies limit our ability to rapidly pursue these developments. Strikingly, no specific inhibitors of histone methylation exist. This proposal seeks to eliminate this limitation by developing a simple, quantitative high throughput assay capable of individually measuring the activity of each of the histone H3 lysine methylating enzymes. To this goal the specific aims are: 1) Migrate existing histone methyltransferase assays into a high throughput format using competitive fluorescence polarization. This aim will combine existing technologies and reagents into a sensitive and rapid assay. The assay will be initially utilized and further tested on the NCI Structural Diversity set of compounds to identify lead compounds for drug discovery. [unreadable] [unreadable]